Q: why is white rice more fatteining than brown rice even though the GI is nearly identical?

A: Neither I nor anyone else can explain it fully simply because the human body is so incredibly complex. Like I said in http://www.mikesfitness.com/content/replacing-high-glycemic-carbs-with-l... the conversion of food carbohydrates into glucose is just one step of many, so it's to be expected that it doesn't tell the whole story. The difference between white and brown rice lies in the fact that brown rice has all of its original layers except the outermost hull. White rice, on the other hand, has the bran layer, germ layer, and the aleurone layer (containing essential fats) removed. Those three layers contain almost all of vitamins, minerals, and fiber which make brown rice the superior choice, both health-wise and fatloss-wise. Those same minerals, vitamins, essential fats, and fiber are also responsible for the fact that brown rice is significantly less fattening than white rice. Why and how exactly nobody can tell you, though undoubtedly its extra fiber plays a role. If and when the entire reason for this difference is complete understood, it'll probably fill a few dozen pages at least.

Consider this -- it's merely an outline of metabolic processes that happen inside your muscles, the chemical reactions using proteins, fats, and glucose that drive your muscles. It doesn't even go into digestion, nutrients absorbtion into blood, uptake into muscles or organs or fat storage, or various hormonal interactions that affect all the other processes. The only reason I give this example is to demonstrate the incredible complexity of the human body. It's not reasonable to expect any simple guide like the GI index to give the whole picture. The GI index is just one of many tools that you should use to make informed decisions.